diff --git a/meson.build b/meson.build
index 4384063..73914ef 100644
--- a/meson.build
+++ b/meson.build
@@ -9,19 +9,25 @@ cmake = import('cmake')
 mbedtls_proj = cmake.subproject('mbedtls')
 mbedtls_dep = mbedtls_proj.dependency('mbedcrypto')
 
-executable('ex01', ['src/ex01/main.c', 'src/utils.c'], dependencies: m_dep, include_directories: incdir)
-executable('ex02', ['src/ex02/main.c', 'src/utils.c'], dependencies: m_dep, include_directories: incdir)
-executable('ex03', ['src/ex03/main.c', 'src/utils.c'], dependencies: m_dep, include_directories: incdir)
-executable('ex04', ['src/ex04/main.c', 'src/utils.c'], dependencies: m_dep, include_directories: incdir)
-executable('ex05', ['src/ex05/main.c', 'src/utils.c'], dependencies: m_dep, include_directories: incdir)
-executable('ex06', ['src/ex06/main.c', 'src/utils.c'], dependencies: m_dep, include_directories: incdir)
-executable('ex07', ['src/ex07/main.c', 'src/utils.c'],
+executable('ex01', ['src/ex01/main.c', 'src/io.c'],
+	   dependencies: m_dep, include_directories: incdir)
+executable('ex02', ['src/ex02/main.c', 'src/io.c'],
+	   dependencies: m_dep, include_directories: incdir)
+executable('ex03', ['src/ex03/main.c', 'src/io.c', 'src/frequency.c'],
+	   dependencies: m_dep, include_directories: incdir)
+executable('ex04', ['src/ex04/main.c', 'src/io.c', 'src/frequency.c'],
+	   dependencies: m_dep, include_directories: incdir)
+executable('ex05', ['src/ex05/main.c', 'src/io.c'],
+	   dependencies: m_dep, include_directories: incdir)
+executable('ex06', ['src/ex06/main.c', 'src/io.c', 'src/distance.c', 'src/frequency.c'],
+	   dependencies: m_dep, include_directories: incdir)
+executable('ex07', ['src/ex07/main.c', 'src/io.c'],
 	   dependencies: [m_dep, mbedtls_dep], include_directories: incdir)
-executable('ex08', ['src/ex08/main.c', 'src/utils.c'],
+executable('ex08', ['src/ex08/main.c', 'src/io.c'],
 	   dependencies: [m_dep, mbedtls_dep], include_directories: incdir)
 
 munit_dep = dependency('munit', fallback: ['munit', 'munit_dep'])
 
-tests = executable('tests', ['tests/main.c', 'src/utils.c'], include_directories: incdir,
-		   dependencies: [m_dep, munit_dep])
+tests = executable('tests', ['tests/main.c', 'src/io.c', 'src/distance.c', 'src/frequency.c'],
+		   include_directories: incdir, dependencies: [m_dep, munit_dep])
 test('tests', tests)
diff --git a/src/distance.c b/src/distance.c
new file mode 100644
index 0000000..fca6cd3
--- /dev/null
+++ b/src/distance.c
@@ -0,0 +1,14 @@
+#include <string.h>
+
+unsigned int hamming(size_t len, const unsigned char s1[static len],
+                     const unsigned char s2[static len]) {
+  unsigned int res = 0;
+  for (size_t i = 0; i < len; ++i) {
+    unsigned int n = s1[i] ^ s2[i];
+    while (n) {
+      res += n & 1;
+      n >>= 1;
+    }
+  }
+  return res;
+}
diff --git a/src/distance.h b/src/distance.h
new file mode 100644
index 0000000..a2231e1
--- /dev/null
+++ b/src/distance.h
@@ -0,0 +1,9 @@
+#ifndef DISTANCE_H
+#define DISTANCE_H
+
+#include <string.h>
+
+unsigned int hamming(size_t len, const unsigned char s1[static len],
+                     const unsigned char s2[static len]);
+
+#endif /* DISTANCE_H */
diff --git a/src/ex01/main.c b/src/ex01/main.c
index 849bb30..ad02346 100644
--- a/src/ex01/main.c
+++ b/src/ex01/main.c
@@ -1,4 +1,4 @@
-#include "utils.h"
+#include "io.h"
 #include <stdio.h>
 #include <stdlib.h>
 
diff --git a/src/ex02/main.c b/src/ex02/main.c
index 9bffe7e..1fcd6fc 100644
--- a/src/ex02/main.c
+++ b/src/ex02/main.c
@@ -1,9 +1,8 @@
-#include "utils.h"
+#include "io.h"
 #include <stdio.h>
 #include <stdlib.h>
 
-int main(int argc, char *argv[])
-{
+int main(int argc, char *argv[]) {
   if (argc < 3) {
     printf("Usage: %s <hex1> <hex2>\n", argv[0]);
     return EXIT_FAILURE;
diff --git a/src/ex03/main.c b/src/ex03/main.c
index c82d202..14b8580 100644
--- a/src/ex03/main.c
+++ b/src/ex03/main.c
@@ -1,9 +1,10 @@
-#include "utils.h"
+#include "frequency.h"
+#include "io.h"
 #include <ctype.h>
+#include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <math.h>
 
 int main(int argc, char *argv[]) {
   if (argc < 2) {
diff --git a/src/ex04/main.c b/src/ex04/main.c
index aea2137..aac1631 100644
--- a/src/ex04/main.c
+++ b/src/ex04/main.c
@@ -1,4 +1,5 @@
-#include "utils.h"
+#include "frequency.h"
+#include "io.h"
 #include <ctype.h>
 #include <stdio.h>
 
@@ -37,16 +38,15 @@ int main(int argc, char *argv[]) {
       }
       double score = frequency_score(len, cur);
       if (score < 40.0) {
-        printf("%4u | %c   | %5.1f | ", line_count, c,
-               score);
+        printf("%4u | %c   | %5.1f | ", line_count, c, score);
         for (size_t i = 0; i < len; ++i) {
-	  if (isprint(cur[i])) {
-	    putchar(cur[i]);
-	  } else if (cur[i] == '\n') {
-	    printf("\\n");
-	  }
+          if (isprint(cur[i])) {
+            putchar(cur[i]);
+          } else if (cur[i] == '\n') {
+            printf("\\n");
+          }
         }
-	printf("\n");
+        printf("\n");
       }
     }
   }
diff --git a/src/ex05/main.c b/src/ex05/main.c
index c89215d..b19bab9 100644
--- a/src/ex05/main.c
+++ b/src/ex05/main.c
@@ -1,4 +1,4 @@
-#include "utils.h"
+#include "io.h"
 #include <ctype.h>
 #include <stdio.h>
 #include <string.h>
diff --git a/src/ex06/main.c b/src/ex06/main.c
index 339b883..46c63d3 100644
--- a/src/ex06/main.c
+++ b/src/ex06/main.c
@@ -1,4 +1,6 @@
-#include "utils.h"
+#include "distance.h"
+#include "frequency.h"
+#include "io.h"
 #include <ctype.h>
 #include <math.h>
 #include <stdio.h>
diff --git a/src/ex07/main.c b/src/ex07/main.c
index ffec533..849ee8b 100644
--- a/src/ex07/main.c
+++ b/src/ex07/main.c
@@ -1,5 +1,5 @@
+#include "io.h"
 #include "mbedtls/aes.h"
-#include "utils.h"
 #include <ctype.h>
 #include <math.h>
 #include <stdio.h>
diff --git a/src/ex08/main.c b/src/ex08/main.c
index 286b45c..6281a74 100644
--- a/src/ex08/main.c
+++ b/src/ex08/main.c
@@ -1,4 +1,4 @@
-#include "utils.h"
+#include "io.h"
 #include <stdio.h>
 
 #define BUF_SIZE 1024
diff --git a/src/frequency.c b/src/frequency.c
new file mode 100644
index 0000000..388299c
--- /dev/null
+++ b/src/frequency.c
@@ -0,0 +1,65 @@
+#include "frequency.h"
+#include <ctype.h>
+#include <math.h>
+#include <string.h>
+
+double frequency_score(size_t len, const char buf[static len]) {
+  static const double english_freqs[27] = {
+      // A-Z
+      0.0855, 0.0160, 0.0316, 0.0387, 0.01210, 0.0218, 0.0209, 0.0496, 0.0733,
+      0.0022, 0.0081, 0.0421, 0.0253, 0.0717, 0.0747, 0.0207, 0.0010, 0.0633,
+      0.0673, 0.0894, 0.0268, 0.0106, 0.0183, 0.0019, 0.0172, 0.0011,
+      // space
+      0.19182};
+
+  // static const double english_freqs[27] = {
+  //     // A-Z
+  //     0.08167, 0.01492, 0.02782, 0.04253, 0.12702, 0.02228, 0.02015, 0.06094,
+  //     0.06966, 0.00153, 0.00772, 0.04025, 0.02406, 0.06749, 0.07507, 0.01929,
+  //     0.00095, 0.05987, 0.06327, 0.09056, 0.02758, 0.00978, 0.02360, 0.00150,
+  //     0.01974, 0.00074,
+  //     // space
+  //     0.19182};
+
+  unsigned int counts[27] = {0};
+  for (size_t i = 0; i < len; ++i) {
+    if (!isprint(buf[i]) && buf[i] != '\n') {
+      // If character is not printable, it's definitely not English.
+      return INFINITY;
+    }
+    if (buf[i] == ' ') {
+      counts[26]++;
+      continue;
+    }
+    unsigned char c = tolower(buf[i]) - 'a';
+    if (c < 26) {
+      counts[c]++;
+    }
+  }
+
+  double chi2 = 0;
+  for (size_t i = 0; i < 27; ++i) {
+    double expected = len * english_freqs[i];
+    chi2 += pow(counts[i] - expected, 2) / expected;
+  }
+  return chi2;
+}
+
+char best_single_char_xor_key(size_t len, unsigned char buf[static len]) {
+  char cur[len];
+  double min_score = INFINITY;
+  char key = 'X';
+
+  for (char c = 32; c < 127; ++c) {
+    for (size_t i = 0; i < len; ++i) {
+      cur[i] = buf[i] ^ c;
+    }
+    double score = frequency_score(len, cur);
+    if (score < min_score) {
+      min_score = score;
+      key = c;
+    }
+  }
+
+  return key;
+}
diff --git a/src/frequency.h b/src/frequency.h
new file mode 100644
index 0000000..770477d
--- /dev/null
+++ b/src/frequency.h
@@ -0,0 +1,9 @@
+#ifndef FREQUENCY_H
+#define FREQUENCY_H
+
+#include <string.h>
+
+double frequency_score(size_t len, const char buf[static len]);
+char best_single_char_xor_key(size_t len, unsigned char buf[static len]);
+
+#endif /* FREQUENCY_H */
diff --git a/src/io.c b/src/io.c
new file mode 100644
index 0000000..f970ca9
--- /dev/null
+++ b/src/io.c
@@ -0,0 +1,73 @@
+#include "io.h"
+#include <ctype.h>
+#include <string.h>
+
+unsigned char hex_to_byte(const char c) {
+  if (isdigit(c)) {
+    return c - '0';
+  }
+  return 10 + c - 'a';
+}
+
+size_t hex_to_bytes(unsigned char out[static 1], const char hex[static 1]) {
+  for (size_t i = 0; i < strlen(hex); ++i) {
+    char c = tolower(hex[i]);
+    unsigned char value = hex_to_byte(c);
+    if (i % 2 == 0) {
+      value <<= 4;
+    }
+    out[i / 2] += value;
+  }
+  return strlen(hex) / 2 + strlen(hex) % 2;
+}
+
+static const char base64_table[65] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+char *bytes_to_base64(char out[static 4], const unsigned char in[static 3],
+                      size_t len) {
+  for (size_t i = 0; i < len - 2; i += 3) {
+    size_t j = i / 3 * 4;
+    out[j] = base64_table[in[i] >> 2];
+    out[j + 1] = base64_table[((in[i] & 0x03) << 4) | (in[i + 1] >> 4)];
+    out[j + 2] = base64_table[((in[i + 1] & 0x0f) << 2) | (in[i + 2] >> 6)];
+    out[j + 3] = base64_table[in[i + 2] & 0x3f];
+  }
+  return out;
+}
+
+size_t base64_to_bytes(unsigned char out[static 3], const char in[static 4]) {
+  char decoding_table[256] = {0};
+  for (size_t i = 0; i < 64; ++i) {
+    decoding_table[(unsigned char)base64_table[i]] = i;
+  }
+
+  size_t in_length = strlen(in);
+  if (in_length % 4 != 0) {
+    return 0;
+  }
+
+  size_t i = 0;
+  for (size_t j = 0; j < in_length - 3;) {
+    unsigned char sextet1 =
+        in[j] == '=' ? 0 : decoding_table[(unsigned char)in[j]];
+    unsigned char sextet2 =
+        in[j + 1] == '=' ? 0 : decoding_table[(unsigned char)in[j + 1]];
+    unsigned char sextet3 =
+        in[j + 2] == '=' ? 0 : decoding_table[(unsigned char)in[j + 2]];
+    unsigned char sextet4 =
+        in[j + 3] == '=' ? 0 : decoding_table[(unsigned char)in[j + 3]];
+
+    out[i] = sextet1 << 2;
+    out[i] += sextet2 >> 4;
+    out[i + 1] = sextet2 << 4;
+    out[i + 1] += sextet3 >> 2;
+    out[i + 2] = sextet3 << 6;
+    out[i + 2] += sextet4;
+
+    j += 4;
+    i += 3;
+  }
+
+  return i;
+}
diff --git a/src/io.h b/src/io.h
new file mode 100644
index 0000000..9414fa9
--- /dev/null
+++ b/src/io.h
@@ -0,0 +1,12 @@
+#ifndef IO_H
+#define IO_H
+
+#include <stdlib.h>
+
+unsigned char hex_to_byte(const char c);
+size_t hex_to_bytes(unsigned char out[static 1], const char hex[static 1]);
+char *bytes_to_base64(char out[static 4], const unsigned char in[static 3],
+                      size_t len);
+size_t base64_to_bytes(unsigned char out[static 3], const char in[static 4]);
+
+#endif /* IO_H */
diff --git a/src/utils.c b/src/utils.c
deleted file mode 100644
index a3f80ff..0000000
--- a/src/utils.c
+++ /dev/null
@@ -1,148 +0,0 @@
-#include "utils.h"
-#include <ctype.h>
-#include <math.h>
-#include <string.h>
-
-unsigned char hex_to_byte(const char c) {
-  if (isdigit(c)) {
-    return c - '0';
-  }
-  return 10 + c - 'a';
-}
-
-size_t hex_to_bytes(unsigned char out[static 1], const char hex[static 1]) {
-  for (size_t i = 0; i < strlen(hex); ++i) {
-    char c = tolower(hex[i]);
-    unsigned char value = hex_to_byte(c);
-    if (i % 2 == 0) {
-      value <<= 4;
-    }
-    out[i / 2] += value;
-  }
-  return strlen(hex) / 2 + strlen(hex) % 2;
-}
-
-static const char base64_table[65] =
-    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
-
-char *bytes_to_base64(char out[static 4], const unsigned char in[static 3],
-                      size_t len) {
-  for (size_t i = 0; i < len - 2; i += 3) {
-    size_t j = i / 3 * 4;
-    out[j] = base64_table[in[i] >> 2];
-    out[j + 1] = base64_table[((in[i] & 0x03) << 4) | (in[i + 1] >> 4)];
-    out[j + 2] = base64_table[((in[i + 1] & 0x0f) << 2) | (in[i + 2] >> 6)];
-    out[j + 3] = base64_table[in[i + 2] & 0x3f];
-  }
-  return out;
-}
-
-size_t base64_to_bytes(unsigned char out[static 3], const char in[static 4]) {
-  char decoding_table[256] = {0};
-  for (size_t i = 0; i < 64; ++i) {
-    decoding_table[(unsigned char)base64_table[i]] = i;
-  }
-
-  size_t in_length = strlen(in);
-  if (in_length % 4 != 0) {
-    return 0;
-  }
-
-  size_t i = 0;
-  for (size_t j = 0; j < in_length - 3;) {
-    unsigned char sextet1 =
-        in[j] == '=' ? 0 : decoding_table[(unsigned char)in[j]];
-    unsigned char sextet2 =
-        in[j + 1] == '=' ? 0 : decoding_table[(unsigned char)in[j + 1]];
-    unsigned char sextet3 =
-        in[j + 2] == '=' ? 0 : decoding_table[(unsigned char)in[j + 2]];
-    unsigned char sextet4 =
-        in[j + 3] == '=' ? 0 : decoding_table[(unsigned char)in[j + 3]];
-
-    out[i] = sextet1 << 2;
-    out[i] += sextet2 >> 4;
-    out[i + 1] = sextet2 << 4;
-    out[i + 1] += sextet3 >> 2;
-    out[i + 2] = sextet3 << 6;
-    out[i + 2] += sextet4;
-
-    j += 4;
-    i += 3;
-  }
-
-  return i;
-}
-
-double frequency_score(size_t len, const char buf[static len]) {
-  static const double english_freqs[27] = {
-      // A-Z
-      0.0855, 0.0160, 0.0316, 0.0387, 0.01210, 0.0218, 0.0209, 0.0496, 0.0733,
-      0.0022, 0.0081, 0.0421, 0.0253, 0.0717, 0.0747, 0.0207, 0.0010, 0.0633,
-      0.0673, 0.0894, 0.0268, 0.0106, 0.0183, 0.0019, 0.0172, 0.0011,
-      // space
-      0.19182};
-
-  // static const double english_freqs[27] = {
-  //     // A-Z
-  //     0.08167, 0.01492, 0.02782, 0.04253, 0.12702, 0.02228, 0.02015, 0.06094,
-  //     0.06966, 0.00153, 0.00772, 0.04025, 0.02406, 0.06749, 0.07507, 0.01929,
-  //     0.00095, 0.05987, 0.06327, 0.09056, 0.02758, 0.00978, 0.02360, 0.00150,
-  //     0.01974, 0.00074,
-  //     // space
-  //     0.19182};
-
-  unsigned int counts[27] = {0};
-  for (size_t i = 0; i < len; ++i) {
-    if (!isprint(buf[i]) && buf[i] != '\n') {
-      // If character is not printable, it's definitely not English.
-      return INFINITY;
-    }
-    if (buf[i] == ' ') {
-      counts[26]++;
-      continue;
-    }
-    unsigned char c = tolower(buf[i]) - 'a';
-    if (c < 26) {
-      counts[c]++;
-    }
-  }
-
-  double chi2 = 0;
-  for (size_t i = 0; i < 27; ++i) {
-    double expected = len * english_freqs[i];
-    chi2 += pow(counts[i] - expected, 2) / expected;
-  }
-  return chi2;
-}
-
-unsigned int hamming(size_t len, const unsigned char s1[static len],
-                     const unsigned char s2[static len]) {
-  unsigned int res = 0;
-  for (size_t i = 0; i < len; ++i) {
-    unsigned int n = s1[i] ^ s2[i];
-    while (n) {
-      res += n & 1;
-      n >>= 1;
-    }
-  }
-  return res;
-}
-
-char best_single_char_xor_key(size_t len, unsigned char buf[static len]) {
-  char cur[len];
-  double min_score = INFINITY;
-  char key = 'X';
-
-  for (char c = 32; c < 127; ++c) {
-    for (size_t i = 0; i < len; ++i) {
-      cur[i] = buf[i] ^ c;
-    }
-    double score = frequency_score(len, cur);
-    if (score < min_score) {
-      min_score = score;
-      key = c;
-    }
-  }
-
-  return key;
-}
diff --git a/src/utils.h b/src/utils.h
deleted file mode 100644
index 6e900bf..0000000
--- a/src/utils.h
+++ /dev/null
@@ -1,14 +0,0 @@
-#ifndef UTILS_H
-#define UTILS_H
-
-#include <stdlib.h>
-
-unsigned char hex_to_byte(const char c);
-size_t hex_to_bytes(unsigned char out[static 1], const char hex[static 1]);
-char *bytes_to_base64(char out[static 4], const unsigned char in[static 3], size_t len);
-size_t base64_to_bytes(unsigned char out[static 3], const char in[static 4]);
-double frequency_score(size_t len, const char buf[static len]);
-unsigned int hamming(size_t len, const unsigned char s1[static len], const unsigned char s2[static len]);
-char best_single_char_xor_key(size_t len, unsigned char buf[static len]);
-
-#endif /* UTILS_H */
diff --git a/tests/main.c b/tests/main.c
index 28b170a..84900b0 100644
--- a/tests/main.c
+++ b/tests/main.c
@@ -1,6 +1,8 @@
 #define MUNIT_ENABLE_ASSERT_ALIASES
+#include "distance.h"
+#include "frequency.h"
+#include "io.h"
 #include "munit.h"
-#include "utils.h"
 #include <math.h>
 #include <stdlib.h>